Conventionally, improvement in heat resistance, and an increase in flame retardancy of printed wiring boards used in electronics have been achieved by improving a glass transition temperature (Tg) or the like. In recent years, particularly in the field of small electronics such as mobile devices, following the reduction in size and thickness of devices, and an increase in the number of functions of devices, market demand for a further reduction in permittivity and CTE (coefficient of thermal expansion) of printed wiring boards has been increasing. In general, an epoxy resin composition is used as an insulating material for a printed wiring board. In this epoxy resin composition, a phenol-based curing agent, a diamine-based curing agent, a cyanate-based curing agent, an acid anhydride-based curing agent, or the like is used as a curing agent for the epoxy resin. Of these various curing agents, it is known that the acid anhydride-based curing agent is effective in achieving a reduction in permittivity. Conventionally, a polyfunctional acid anhydride-based compound having a plurality of acid anhydride rings in one molecule, styrene-maleic acid copolymer (SMA), or the like has been used as the acid anhydride-based curing agent. For example, Patent Document 1 discloses that a copolymer (SMA) including styrene and maleic anhydride as essential components is used as the acid anhydride-based curing agent.